Attention has been focused on a technique for forming a transistor using a semiconductor thin film (also referred to as a thin film transistor (TFT)). The transistor is applied to a wide range of electronic devices such as an integrated circuit (IC) or an image display device. A silicon-based semiconductor material is widely known as a material for a semiconductor thin film applicable to a transistor. As another example, an oxide semiconductor has been attracting attention.
For example, a transistor using an amorphous oxide containing indium (In), gallium (Ga), and zinc (Zn) for a channel formation region of a transistor is disclosed (see Patent Document 1).
Further, it is known that oxygen is released from an oxide semiconductor during a manufacturing process, so that an oxygen vacancy is formed (see Patent Document 2).